A one-pot and single-step reduction process for producing antioxidized copper fine particles will be described. This process can be carried out at room temperature, and size range is quite wide, from 190 nm to 1 mu m by varying the amount of gelatin, the stabilizing reagent. From SEM images it is revealed that higher loading of gelatin gave larger but relatively uniform particles. However, XRD patterns indicated that the large particles were composed of smaller particles; that is, they had a "particle-in-particle" structure. Cross-sectional TEM image strongly supports this structure and indicates that gelatin is a good antioxidizing coating material which kept 5-nm copper metallic.